This invention concerns a load responsive valve for rolling stock which operates the brake control automatically according to the load on the rolling stock.
Brake control is very important in operating rolling stock, especially with automatic train operation (ATO) and automatic train control (ATC). A brake which can automatically respond to the rolling stock load is essential. For example, in the case of railroad rolling stock which has (an) air spring car(s), a load responsive valve has been designed and has been used as follows. Using air spring pressure which changes in proportion to the rolling stock load, the air spring pressure (control pressure) and the brake output pressure correspond to each other, since the brake output pressure is determined by the air spring pressure. The following is a description of a conventional load responsive valve based on FIG. 1. Control pressure responding to the rolling stock load was set as (the) air spring pressure, and air was used as the pressurized medium.
An input chamber 6 is formed between the top of the main body 1 and the upper wall 2. The supply valve seat 11 provided on the upper wall 2 has a supply valve 13, and a supply spring 14 attached to the supply valve. A hollow-cylindrical discharge valve 15 can slide up and down through the detached wall 3 without leaking any pressure through the wall. Below the detached wall 3, around the discharge valve 15, a plate-type balance piston 4 is installed. The discharge valve 15 forms a discharge valve seat 16 at its upper end. It is positioned inside the supply valve seat 11 and faces the supply valve 13. The inner hole 17 of the discharge valve 15 opens at the lower end to the discharge chamber 9 which is described later. In the detached wall 3, there is a connecting hole 12 which connects the output chamber 7 formed between the detached wall 3 and the upper wall 2, and the balance chamber 8 formed between the detached wall 3 and the balance piston 4. Below the balance piston 4 above the plate-type control piston 5, there is a discharge chamber 9 placed with a control spring 18. The control chamber 10 is formed at the bottom of the body 1 below the control piston 5. The input chamber 6 is connected to the pressurized air source (not shown) through the input pipe 19. The output chamber 7 is connected to the relay valve 26 of the brake control system (not shown) through the output pipe 20. The discharge chamber 9 is connected to the atmosphere through the discharge port 21. The control chamber 10 is connected to the air spring (not shown) by the brake air reservoir 23 and the throttle 24 through the control pipe 22, 25.
When the brake is released and the rolling stock is running, pressurized air from the pressurized air source flows into the input chamber 6 through the input pipe 19. The pressurized air of the air spring flows into the control chamber 10 through the control pipe 25, the throttle 24, the braking air reservoir 23, and the control pipe 22. Therefore, the control piston 5 moves upward. The balance piston 4 and the discharge valve 15 are pushed upward by the control spring 18. The discharge valve seat 16 of the discharge valve 15 comes into contact with the bottom of the supply valve 13 and closes the open area. The discharge valve 15 moves up even higher and the supply valve is moved away from the supply valve seat 11. As a result, the pressurized air in the input chamber 6 goes through the supply valve seat 11, flows into the output chamber 7, and is supplied to the relay valve 26 of the brake control system through the output pipe 20. On the other hand, pressurized air in the output chamber 7 flows into the balance chamber 8 through the connecting hole 12 of the detached wall 3, and is effective to push down the balance piston 4. Thus, the upward force which actuates the control piston 5 and the downward force which actuates the balance piston 4 oppose each other by means of the control spring 18, and when the force which actuates the balance piston 4 approximates the total value of the force which actuates the control piston 5 and the tension of the control spring 18, the balance piston 4 moves downward, and at the same time, the discharge valve 15 also moves downward. Therefore, the supply valve 13 comes down with the discharge valve seat 16 being contacted, and it comes into contact with the supply valve seat 11. As a result, the pressure stops rising in the output chamber 7 and in the balance chamber, and the force which actuates the balance piston 4 is balanced with the total value of the force which actuates the control piston 5 and the tension of the control spring 18. Thus, the pressure in the output chamber 7 which is supplied to the brake control system is proportional to the air spring pressure.
At this time, when the pressure of the air spring rises, the pressure in the control chamber 10 rises, and the control piston 5 pushes up the discharge valve 15 as well as the balance piston 15 by means of the control spring 18. Therefore, the supply valve 13 is moved away from the supply valve seat 11, and the supplied air enters the output chamber 7 and the pressure in the balance chamber 8 rises. As a result, the balance piston 4 is pushed down and the pressure becomes proportional by having the supply valve 13 sit on the supply valve seat 11. On the other hand, when the air spring pressure falls, the pressure in the control chamber 10 falls, and the balance piston 4 pushes down the control piston 5 through the control spring 18. Therefore, the discharge valve seat 16 of the discharge valve 15 moves away from the supply valve 13, and the pressurized air in the balance chamber 8 is discharged through the inner hole 17, the discharge chamber 9, and the discharge port 21 into the atmosphere. As a result, the pressure in the balance chamber 8 falls, and when it becomes proportional to the pressure in the control chamber 10, the balance piston 4 is pushed up by the control piston 5. The discharge valve seat 16 comes into a contact with the supply valve 13, and the pressurized air in the balance chamber 8 stops discharging to become proportional. Thus, pressurized air which is proportional to the pressure in the control chamber 10 is charged to the brake control system through the output pipe 20.
On the other hand, the air spring pressure fluctuates not only with the load on the rolling stock but also depending on the railroad conditions. Therefore, when a change in the air spring pressure is transmitted to the control chamber 10, the control piston 5 and the balance piston 4 move their positions responding to the pressure change, and the discharge valve 15 also moves up and down depending on the change. The supply valve seat 11 and the discharge valve seat 16 are opened and closed by the supply valve 13, the pressurized air in the output chamber 7 is supplied and discharged, and the output pressure fluctuates.
These position changes of the control piston 5 and the balance piston 4 hasten fatigue and abrasion on both pistons 4, 5, as well as on the discharge valve 15 and the supply valve 13. They also waste the pressurized air unnecessarily during the rolling stock operation.
As shown in FIG. 1, the throttle 24 and the brake air reservoir 23 are placed as buffers between the air spring and the control chamber 10 in order to reduce sudden pressure changes from the air spring, then pressure enters the control chamber 10. Therefore, sudden air spring pressure changes are not transmitted to the control chamber 10.
However, this type of buffer cannot absorb slow pressure changes, but changes the position of the control piston 5. When the rolling stock is running, this pressure change creates a constant position change of the balance piston 4. The discharge valve 15 keeps opening and closing the supply valve seat 11 and the discharge valve seat 16, and pressurized air is wasted every time it is supplied and discharged. The frequent position changes cause the wear and tear of both pistons 4, 5. Furthermore, this type of load responsive valve requires space and a complicated design for a brake air reservoir 23 and a throttle 24, and it also causes a weight problem. These are the shortcomings of the conventional load responsive valve.